Regarding the 10 bore chambers, my W.J.Jeffrey heavy ten HG circa 1895, 34" 11 1/2 lbs. is stamped on the underside of the barrels
"for 3 1/4" Perfect brass cases" and the original proofs marks for bore size are 10/2, ie. overbored to handle the thin brass case with oversize wads and heavier shot charge. I guess the original magnum 10


Better to keep your mouth shut and be thought stupid,than open it and confirm.